A numerical model to predict the powder–binder separation during micro-powder injection molding

The micro-powder injection molding (micro-PIM) process has the potential to bridge the gap between the design and manufacturing of micro-components that are often used in small and handy devices. Numerical modeling helps to analyze and overcome various difficulties of micro-PIM. In the present work, a numerical model is developed to predict the powder–binder separation (a common defect in PIM and especially severe in micro-PIM) during the injection of an alumina feedstock. A powder–binder separation criterion is proposed dealing with applied injection pressure and friction force between the powder and binder. An indirect comparison of feedstock travel time between two locations is used to validate the model. The predicted segregation from the simulated result is supported by a qualitative experimental measurement. The developed model can be used to optimize injection parameters to get a defect-free product.     

Mg gas infiltration for the fabrication of MgB2 pellets using nanosized and microsized B powders

MgB₂ superconductor pellets were synthesized through Mg gas infiltration method using nanosized- and microsized B powders. There was a marked difference in the superconducting properties of the two samples, particularly in the pinning force and dominant pinning mechanism. The microstructures of the samples were observed using HR-TEM and STEM-HAADF, and the results showed that the primary reason for the difference in the superconducting properties is the distribution of the nanosized second-phase particle MgO. Additionally, a feasible reaction model for the Mg gas infiltration method was established. Compared to the Mg liquid infiltration method, the gas infiltration showed better penetrability ability with a small amount of residual Mg. This study presents a novel synthesis process to fabricate an MgB₂ pellet with superior density and superconducting properties. This method can be used in multiple applications such as superconducting bearings, compact superconductor magnets, and magnetic shielding.     

Multi-dimensional modeling of mixture preparation in a direct injection engine fueled with gaseous hydrogen

With the recent advances of direct injection (DI) technology, introducing hydrogen into the combustion chamber through DI is being considered as a viable approach to circumvent backfire and pre-ignition encountered in early generations of hydrogen engines. As part of a broader vision to develop a robust numerical model to study hydrogen spark ignition (SI) combustion in internal combustion (IC) engines, the present numerical investigation focuses on mixture preparation in a hydrogen DI SI engine. This study is carried out with a single hole injector with gaseous hydrogen injected at 100 bar injection pressure. Simulations are carried out for high and low tumble configurations and validated against optical data acquired from planar laser induced fluorescence (PLIF) measurements. Varying mesh configurations are investigated for the impact on in-cylinder mixture distribution. A particular emphasis is placed on the effect of nozzle geometry and mesh orientation near the wall. Overall, the computational model is found to predict the mixture distribution in the combustion cylinder reasonably well. The results showed that the alignment of mesh with the flow direction is important to achieve good agreement between numerical analysis and optical measurement data.     

Predictive process mapping for laser powder bed fusion: A review of existing analytical solutions

One of the main challenges in the laser powder bed fusion (LPBF) process is making dense and defect-free components. These porosity defects are dependent upon the melt pool geometry and the processing conditions. Power-velocity (PV) processing maps can aid in visualizing the effects of LPBF processing variables and mapping different defect regimes such as lack-of-fusion, under-melting, balling, and keyholing. This work presents an assessment of existing analytical equations and models that provide an estimate of the melt pool geometry as a function of material properties. The melt pool equations are then combined with defect criteria to provide a quick approximation of the PV processing maps for a variety of materials. Finally, the predictions of these processing maps are compared with experimental data from the literature. The predictive processing maps can be computed quickly and can be coupled with dimensionless numbers and high-throughput (HT) experiments for validation. The present work provides a boundary framework for designing the optimal processing parameters for new metals and alloys based on existing analytical solutions.     

Effect of coral sand powders and seawater salinity on the impact mechanical properties of cemented coral sand

Coral sand is one kind of the important building materials in coral reef engineering practice. The use of cement as a stabilizing agent can significantly improve the mechanical properties of coral sands and is widely applied in the subbase engineering construction in coral reef islands. Cement-stabilized coral sand structures may contain high contents of fine coral particles and salinity because of the high crushability of coral sands and the existence of seawater surrounding them. In this study, the effects of coral sand powders and seawater salinity on the dynamic mechanical properties of cemented coral sand (CCS) were investigated through the split Hopkinson pressure bar (SHPB) tests and Scanning Electron Microscope (SEM) analysis. It was found that the strength (i.e., the peak stress) of CCS specimens increased firstly and then decreased with the increase of powder content. The specimens reached the maximum peak stress when 3% powder content was included. The initial improvement of CCS strength was attributed to the pore-filling effect of coral powders, namely, the micro pores of the CCS specimens could be more effectively filled with higher percentages of coral powders being used in the experiments. However, excessive coral powders resulted in the reduction of specimen strength because these powders could easily be cemented into agglomerates by absorbing water from the specimens. These agglomerates could reduce the cementation strength between the coarse coral particles and the cement. Meanwhile, the peak stress of CCS specimens was found to be negatively correlated with the average strain rate and the ultimate strain. The degree of specimen fracture was found to be correlated with the amount of specific energy absorption during the tests. Furthermore, the “sulfate attack” caused by the inclusion of salinity of water had different influences on the CCS specimens with different coral powder contents. The ettringite and gypsum produced in “sulfate attack” could fill the pores and lead to cracking of the specimens, significantly affecting the specimen strength.     

注射模生产中智能化控制及应用

分析了注射模生产的现状，针对其生产中智能化调控应用方面的不足，提出模内参数的自适应调节方案，还介绍了自适应工作的原理、可调参数种类、逻辑推理等，并实际验证了基于注塑设备联网集成工艺数据下注射模成型工艺自适应调节的可行性。     

Experimental study and numerical modeling of mixing by air injection in yield stress fluids using the OpenFOAM software

Mixing by gas injection is an operation used in industrial processes such as wastewater treatment, metallurgy, or methanization in which pressurized gas is injected into a fluid in order to reduce concentrations and temperatures gradients. This study demonstrates how the CFD toolbox OpenFOAM can be used to simulate such flows. Experimental measurements and observations have been performed on a pilot-scale reactor where pressurized air is injected in a yield stress fluid. The volume of fluid method and an adaptive mesh with refinement at the interface have been used to track the gas inclusions. The numerical model accuracy has been assessed by comparing experimental and numerical results related to the bubble's frequency, dimensions, and rising velocities as well as the fluid recirculation, yielded, and unyielded regions in the tank. The influence of injection parameters such as the injection flow rate and the fluid rheological parameters has been quantified.     

汽车加油口双色注射模设计

分析了汽车加油口塑件结构,确定了注射成型方案、进胶方式,并介绍了通过滑块与开模动作配合实现塑件脱模的过程。     

Laboratory Studies to Determine Suitable Chemicals to Improve Oil Recovery from Garzan Oil Field

Garzan oil field is located at the south east of Turkey. It is a mature oil field and the reservoir is fractured carbonate reservoir. After producing about 1% original oil in place (OOIP) reservoir pressure started to decline. Waterflooding was started in order to support reservoir pressure and also to enhance oil production in 1960. Waterflooding improved the oil recovery but after years of flooding water breakthrough at the production wells was observed. This increased the water/oil ratio at the production wells. In order to enhance oil recovery again different techniques were investigated. Chemical enhanced oil recovery (EOR) methods are gaining attention all over the world for oil recovery. Surfactant injection is an effective way for interfacial tension (IFT) reduction and wettability reversal. In this study, 31 different types of chemicals were studied to specify the effects on oil production. This paper presents solubility of surfactants in brine, IFT and contact angle measurements, imbibition tests, and lastly core flooding experiments. Most of the chemicals were incompatible with Garzan formation water, which has high divalent ion concentration. In this case, the usage of 2-propanol as co-surfactant yielded successful results for stability of the selected chemical solutions. The results of the wettability test indicated that both tested cationic and anionic surfactants altered the wettability of the carbonate rock from oil-wet to intermediate-wet. The maximum oil recovery by imbibition test was reached when core was exposed 1-ethly ionic liquid after imbibition in formation water. Also, after core flooding test, it is concluded that considerable amount of oil can be recovered from Garzan reservoir by waterflooding alone if adverse effects of natural fractures could be eliminated.     

高应力软岩巷道锚注一体化联合支护技术应用

介绍了国家专利注锚剂、中空注浆锚索等产品,以国家能源麦朵山煤矿11采区2煤辅助运输巷为研究对象,采用数值模拟、理论分析、现场测试及井下试验相结合的综合研究方法,对11采区2煤辅助运输巷采用锚注一体联合支护技术,来实现对岩体裂隙注浆,使浆料与岩体结为一体,在围岩与支护体共同作用过程中,实现强岩增荷的作用,维护巷道的稳定性,实现工作面的安全生产。